Special-purpose local area networks are prevalent in manufacturing, monitoring, process control, and other industrial environments. Increasingly, such networks are digital rather than analog, due to the increased carrying capacity and ease of set up and maintenance of digital networks. For example, analog networks often require dedicated wire harnesses to each device in the network in a hub and spoke topology, whereas digital networks may take advantage of the increased informational capacity of digital transmission by employing common main lines in a circular or other shared data link arrangement. A network used in the context of an industrial process to control or monitor industrial devices is commonly referred to as a fieldbus network, or simply as a fieldbus.
There exist a number of popular choices with respect to reasonably standardized industrial fieldbus network types, including predominantly DeviceNet, Profibus, and Foundation Fieldbus. DeviceNet is based on the concept of a controller area network (CAN) and is usually configured to interface with fairly simple industrial devices, but may also interface with more complex bus nodes such as controllers. Profibus, and in particular Profibus-DP, is a commonly used digital network standard that facilitates, among other things, real-time communications between devices and device controllers in the network. Profibus-DP employs a master/slave construct and a token-passing method to control access to the bus. Profibus specifications allow for either a copper or fiber optic physical layer. The Foundation Fieldbus standard is another popular choice for industrial process control networks. The Foundation Fieldbus standard, under development by the Fieldbus Foundation, is distinguished by its focus on distributed rather than centralized control of processes encompassed by the digital network. Many digital process networks other than those described above exist as well, including LonWorks, Interbus-S, Seriplex, and CANopen.